(1) Field of the Invention
The invention relates to a safety syringe, and more particularly to a syringe which is capable of retracting the needle cannula back into the barrel and then fixing the cannula in the barrel, after finishing an injection.
(2) Description of the Prior Art
Syringes are crucial parts for any medical treatment. To avoid accidental serum infection from a contagious disease, disposable syringes are usually used to prevent any syringe from being re-used. Nevertheless, inappropriate handling of the disposable syringes after usage was still seen, and the possibility of infection of a contagious disease for the medical staffs or the cleaners from accidental hurt by the disposed needle cannula always happened. Therefore, the measures of storing the disposed needle cannula and avoiding accidental infection caused from being hurt by the cannula are important topics nowadays while improving the syringe structure.
Generally, after an injection, the needle cannula is immediately retracted into and then stored in the barrel for further handling. For example, in Taiwanese Utility Model Publication No. 165304, an improved safety syringe structure is taught, in which a mating pair are assigned respectively to the extruding ring at end of the barrel and the pushing piston rod on top of the plunger; by providing the mating pair, the injection head having the needle cannula can be engaged with the pushing piston rod and then can be pulled in so as to be stored completely inside the barrel after an injection. In Taiwanese Utility Model Publication No. 356720, a safety syringe is disclosed, in which a threaded part at the bottom end of the needle cannula is introduced to be engaged with a small protruding block on top of the plunger for retracting the needle cannula into the barrel after usage.